Power semiconductors are widely used in various applications. Many devices that use power semiconductors are controlled by low voltage integrated circuits (ICs) of several tens of volts or less. These low-voltage ICs can control high-voltage driver circuits of several hundreds of volts that provide high-voltage power to other electronics. To reduce size and increase performance, the ICs having the low-voltage controls can provide for a direct connection to the high-voltage driver circuits. Accordingly, these ICs have low-voltage regions and high-voltage regions.
The high-voltage regions on the ICs are electrically isolated from the low-voltage regions by an isolation junction to limit the effect of the high voltage on the low-voltage components. Since the high-voltage region and the low-voltage region are on the same piece of silicon, the isolation junction is typically a p-n junction forming a diode between the two regions. One or more control signals, however, travel from the low-voltage control circuits to the high-voltage region. In order for these low-voltage control signals to be appropriate for a high-voltage component, the low-voltage signal is level shifted up to a higher voltage with a level-shift transistor. Caution is exercised in the design of the IC to enable the low-voltage control signal to be level shifted up to the high voltage and enter the high-voltage region without affecting the isolation of the high-voltage region.